The general research objective of the investigator is to delineate the cellular sequences of immunity as they relate to immediate and delayed hypersensitivity states, passive transfer of immunity, homograft reaction (including graft versus host reactions) and tolerance. Since three cell lines (the lymphocytic, plasmocytic and phagocytic) have been implicated as playing major roles in such immune responses, investigative efforts have been concerned with elucidating the origin, life span, fate, function and interrelationships of these cell types. Of especial interest at the present time is the development of in vitro methods for the detection of temporary and permanent states of tolerance as they relate to homograft immunity.